The researchers say cleaning up the sediment in the San Luis Drain could cost millions of dollars using conventional methods, including soil washing, excavation and reburial. In contrast, they say that using plants to remove contaminants ? a process called phytoremediation -- provides one of the most cost-effective methods of cleaning polluted soil available.
"Phytoremediation can help clean up the selenium, but the thing that's holding people up from using plants more widely is that, by and large, they work slowly," said Terry. "So what we want to do is take a plant like Indian mustard, because it can grow quickly -- up to six to seven feet tall -- and it is tolerant to many toxic conditions. It's a good plant for remediation, but we want to see if it's possible to increase its ability to absorb selenium and other pollutants ten-, one hundred-, or even one thousand- fold. This field test is the proof-of-concept showing that we are heading in the right direction."
Researchers like using the Indian mustard plant because it is very efficient at absorbing selenate, the bioavailable form of selenium in the soil. The plant is tricked into absorbing selenate because it is chemically similar to sulfate, an essential nutrient for the plant.
Gary S. Banuelos, a soil scientist with the USDA's ARS and co-lead author of the paper, directed the field tests, which were carried out in Fresno County.
The three types of transgenic plants and the wild-type control plants were transplanted into four 33-by-1 meter field plots, two that contained contaminated sediment from the San Luis Drain and two that contained clean soil.
One line of Indian mustard plants was engineered to produce more of the enzyme adenosine triphosphate sulfurylase (APS). The enzyme is key to the plant's ability to convert selenate into a non-toxic form of selenium, allowing the plant to accumulate more of the contaminant without inc
Source:University of California - Berkeley